This may be a dumb question?

Question

I have just bought a Samsung NV10 and have a question.

I am trying to take long exposure night shots.
I am setting everything up manually but am suffering when it comes to focus.
The NV10 is autofocus and obviously when its dark it does not seem to focus correctly. would the AF light make things better.
With regards apperture I have the choice of two, 7.1 or 2.8. Which one would give me a greater depth of field.
Sorry to sound dumb, but I am trying to work my way upto a DSLR and want to know what I am doing, rather than rely on Auto functions.

Answer 1

First, you definitely need a tripod. If your camera doesn't accept a tripod then you'll need a firm support to sit it on.

Second, set your camera in Manual Mode since you will be setting everything yourself. Make sure the flash is OFF. Your camera has a minimum shutter speed of 15 seconds in Manual Mode so you can use the self-timer to release the shutter.

Suppose you want to photograph a city skyline in the distance after dark. Referring to my FotoSharp (fotosharp.com) Day & Night Exposure Guide, we look at Scene # 14.

ISO 100

f2.8 @ 4 sec.
f4 @ 8 sec.
f5.6 @ 15 sec.

ISO 200

f2.8 @ 2 sec.
f4 @ 4 sec.
f5.6 @ 8 sec.
f8 @ 15 sec.

Your camera has a 3X optical zoom - 35mm to 105mm. At 35mm the maximum f-stop is 2.8; at 105mm it is 5.1 (according to the review at dpreview.com). Check your Owner's Manual to see what the other f-stops are.

The smaller the number (f2.8) the larger the opening in the diaphragm and the less depth of field. However, both the lens and sensor play a role in depth of field, with a wider lens (35mm) having more depth of field and a smaller sensor like your camera has providing more depth of field.

You might find this book helpful: "How Digital Photography Works, Second Edition" by Ron White. You can read a review of it at shutterbug.com - it was in the Dec. 2007 issue of Shutterbug Magazine.

Visit your library and look at the photography magazines they have. Find one or two you really like and subscribe to them.

Answer 2

I don't know about the focus problem, but I have a 35mm SLR (Cannon Rebel GII) and using a smaller aperture will give you a larger field of depth. The smaller the number, the larger the aperture. I would go with a 7.1 for field of depth. Also note that to use a smaller aperture, you will need a longer shutter speed. This shouldn't be a problem for what you are doing, but could interfer with action shots (ie drag races).

Answer 3

A bigger aperture will give less depth of field, in your case f2.8 is the larger aperture. If you use f7.1 the depth of field will be quite big but for long exposure shots you will need to adjust the equivalent film speed to around 100 ASA or the photo will be over exposed. If you are using slow shutter speeds the equivalent film speed needs to be slower.
The focusing can be tricky in low light as some cameras struggle but you might be able to get round this using a manual focus. Have a look in your instruction book.

If you are still having trouble try to join a photography club, the senior member will beonly to happy to pass on their knowledge, failing this have a trip to your nearest photography shop, someone may be willing to help.

Answer 4

If you have the option to turn the focus aid on or off, turn it on. If your subject is more than maybe 15 feet away, set the camera to infinity lock (the mountain icon) instead of autofocus and it will probably be fine, especially if you can select f/7.1.

Answer 5

1

Answer 6

Throw salt up in the air and shoot with a flash at night.